A US woman who shot and killed her husband and two adult children before taking her own life is thought to have committed the shocking crime as a result of being ostracised from the religion she was raised in.

A federal judge sentenced a former Arkansas judge Wednesday to five years in prison — a stiffer punishment than prosecutors recommended — after he admitted giving young male defendants lighter sentences in return for personal benefits that included sexual favours.

Every time I tell a mate I’m doing a story on cryptocurrency, they invariably ask me the same two questions: should they invest their own hard-earned money, and which cryptocurrency will get them a Lamborghini/yacht/island quickest?

In a 60 Minutes online exclusive, reporter Liz Hayes quizzed Australian Prime Minister Malcolm Turnbull on his relationship with the unpredictable Twitter aficionado and US president Donald Trump ahead of their meeting at the White House Friday.

Scientist tries to settle vitamin D hype

The potential general health benefits of vitamin D supplements will at last be clear to Australians but it is going to take five years to find out.

The answer will come from a study of 25,000 people aged 60 to 79, one of the largest projects of its kind in the world.

That vitamin D is important for bone health is accepted, but it is not known what level is needed, says study leader Associate Professor Rachel Neale of the QIMR Berghofer Medical Research Centre.

"People receive conflicting advice about how much sun exposure they need," she says.

"Australia is the skin cancer capital of the world. It may be that a vitamin D supplement is enough."

Prof Neale says the jury is still out on whether vitamin D helps prevent cancer, heart disease and other illnesses.

"There has been enormous hype.

"We know a moderate level of vitamin D is important for our bone health. What we don't know is how much people need and whether supplementing people improves conditions like cancer.

"We hope this study, linking with Medicare records and cancer registries, will provide some definitive answers and advice.

Prof Neale says Australia spends $150 million a year on vitamin D testing, despite the fact that testing is unreliable and "we don't even know what blood level to aim for".

The present recommendation is that people will achieve enough vitamin D with moderate sun exposure, but people who receive no sun exposure should supplement their vitamin D intake with about 400 international units a day, she says.

The outcome of the study could improve the case for mandatory fortification of foods such as bread, Prof Neale says.

Royal College of Pathologists spokesperson Dr Paul Glendenning said the study would help answer important questions.

"It will help determine if there is a case for routine supplementation and routine monitoring of vitamin D.

"We understand that vitamin D has an action in many different parts of the body. This study will help answer whether the amount of vitamin D circulating in the blood is important to those diverse functions.